1. Field of the Disclosure
This disclosure generally relates to a bandgap reference circuit and, more particularly, to a bandgap reference circuit that shuts down the bandgap reference voltage source thereof and provides a source voltage only by a clamp circuit in a suspend mode.
2. Description of the Related Art
FIG. 1 is a conventional power source circuit for providing a source voltage VDD required by a downstream circuit 15. The power source circuit includes a bandgap reference voltage source 11 and a regulator 13. The bandgap reference voltage source 11 provides a stable reference voltage Vref to the regulator 13. The regulator 13 has low static current Iddq to reduce the power consumption and is used to hold the source voltage VDD. However, in a lower power mode, the regulator 13 still requires the power continuously provided by the bandgap reference voltage source 11 to generate the source voltage VDD, such that significant power is still consumed in the low power mode. When this kind of power source circuit is applied to portable electronic devices, the standby time of the portable electronic devices is shortened.
FIG. 2 is another conventional power source circuit. Compared with the one shown in FIG. 1, the power source circuit in FIG. 2 further includes an operational amplifier 22 in addition to a bandgap reference voltage source 21 and a regulator 23. The operational amplifier 22 is used as a clamp circuit and to hold the source voltage VDD in a low power mode. In FIG. 2, although the operational amplifier 22 has low static current Iddq and the regulator 23 can be deactivated in the low power mode, the bandgap reference voltage source 21 still continuously operates in the low power mode.
In addition, in addition to having low static current Iddq (e.g., nano ampere range), the clamp circuit of a bandgap reference circuit has to fulfill the requirements of holding a stable source voltage, a small circuit area and working in an allowable voltage range.
Preferably, the clamp circuit of a bandgap reference circuit does not draw any power from a bandgap reference voltage source in the low power mode. However, it is not easy to achieve this purpose because when the bandgap reference voltage source for providing an accurate reference voltage Vref is shut down and if the reference voltage Vref has a 10% voltage variation, the source voltage VDD provided by the clamp circuit may change more than 10% to exceed the allowable working voltage range.